Nylon Donning Aids consist of two pieces of slippery nylon that slide over one another as you "pull" the donning sheath through the valve opening. The material is very similar to parachutes. Each manufacturer uses a variation of nylon. Some nylon variations are slightly thinner or contain more reinforcement strands. Nylon finishing range from a "crunchy" feel to a light cloth-like feel. It's really a matter of user preference as to which one is better. Some users have commented that having a "crunchy" finish makes it easier for the two nylon layers to slide on one another.
Overall you can expect your nylon parachute bag or pull-style aid to last 3-8 months. Durability ranges and depends on design versus the type of nylon used. Some nylon donning aids have one seam, which is typically more durable than two. In an effort to improve design, some manufacturers have created patterns that transfers stress away from the seams--typically the weakest area on a nylon donning aid. When sizing for a nylon donning aid try to measure accurately. Measuring too small will result in premature wear, typically along a seam or handle.